1. The Field of the Invention
The present invention relates to the field of communication networks and systems. Particularly, this invention relates to interfacing with telecommunication networks requiring a specific interface characteristic for compatible interaction with the network. More specifically, the invention relates to maintaining the interface characteristics and requirements for the dissipation of line side power by a telecommunications terminal interface device, where the line side power is used to provide operational power to line status indicators.
2. Prior State of the Art
Modern data transmission devices such as computers are increasingly used in applications that require exchange of data over a communication network. Some of the more popular communication networks used to propagate data are the well established telephone networks. Such networks were originally designed to accommodate, and therefore propagate, the transmission of voice conversations which include very specific bands of frequencies. Individual countries have implemented unique power and frequency standards relating to their particular implementation of telephone networks.
While the inter-operation specifications differ for national telephone networks, they each require the modulation of computer data in order to comply with the individual specific bandwidth requirements. To facilitate the modulation and the complementary demodulation processes, devices known as modems (MOdulate/DEModulate) have become ubiquitous. In order to compatibly inter-operate with the telephone network, a modem must perform certain xe2x80x9ctelephone handsetxe2x80x9d functions to appear to the telephone network as though it were a legacy telephone handset-compatible device.
Since legacy telephone handsets typically employed electronic circuitry requiring higher power levels, the legacy telephone networks continue to require modem communication devices interfacing therewith, such as modems, to appear to the telephone network as though it were a legacy handset by adhering to specific or specified power ranges which include drawing from the telephone network a specific voltage range as well as a specified range of current from the telephone network.
An example of a legacy telephone handset function is when the modem is xe2x80x9coff-hook.xe2x80x9d Off-hook functionality requires the modem to signal the telephone network that information is either going to be sent by the modem to the telephone network or that the modem is ready to receive information from the telephone network. Telephone network specifications typically require that the modem or other terminal device signal an off-hook condition by drawing or sinking a specified amount of current from the telephone network. Traditionally, such drawn current was utilized by a telephone to xe2x80x9cpowerxe2x80x9d the telephone during use.
Often existing communication networks are commonly used by modem networks, for example the POTS or other internationally similar networks are used to expand connectivity to the network. A POTS network provides an archaic interface that requires a specific amount of off-hook current to be drawn. The typical domestic line side current available is generally in the range of 10 mA to 40 mA, with the preferred range being around 15 mA. Some international telecommunication standards require that a modem""s hold circuit must be able to sink around 120 mA of line current.
In a modem application, where a digital device such as a computer requires appreciable power, the current drawn by the modem is a fraction of the power used by overall digital device. As such, attempts to use the line side power provided by the off-hook condition are typically unnecessary and therefore wasted as the modem functionality derived power either from an external independent power supply or by sharing the power supply of the computer or host device. Furthermore, there is considerable fluctuation of the available line side power, making it difficult to regulate the use of line side power with the delicate modem circuitry.
Another problem facing designers of telecommunication interface devices are the variety of telecommunication specifications propagating worldwide. Those familiar with global telecommunications standards appreciate that various countries have implemented individual and oft times incompatible telephone network standards thereby precluding handsets from inter-operating in various national inter-networks. In the present global climate various countries have settled upon common standards for enabling compatibility between national telephone networks. Once such standard that has been adopted in the majority of European community countries is the TBR21 standard which propagates a specification of standards to which inter-operating terminal equipment, such as telephone handsets and modems, must comply in order to compatibly inter-operate on the European community telephone network.
One such requirement propagated in the specification is a power curve specifying a voltage and current range within which the terminal equipment must inter-operate. Those familiar with the electronic arts appreciate that the voltage and current requirements as propagated in the TBR21 specification are substantial in view of modern, low power electronic circuitry. While electronic devices and circuitry can be implemented in accordance with the higher power specifications of the modem standard, electronic components subjected to higher power levels exhibit earlier power failures and therefore decreased reliability due to the enhanced power. It should be pointed out that while electronic components capable of absorbing higher power levels while maintaining high reliability are available, in mass manufacturing global environments, such high reliability, high power components tend to be impractical due to their high cost and larger physical dimensions, especially in view of an ever increasing miniaturization of electronics.
In the advent of miniaturization, computers have become increasingly more integrated and as such have become more mobile and portable. One overriding design concern with portable computers is power management. In a portable environment, all of the operating power for the computer and any peripheral devices, such as modems, must be resident within the computer. Hence, portable computer batteries are heavily taxed by all of the attached peripheral devices. Therefore, the inefficient use of available line side power affects the overall performance of the digital system by increasing the overall power usage and decreasing the battery life, resulting in a overall higher power dissipation in the hold circuit. Specifically, power is used from the computer battery to indicate the line status of the modem and power is dissipated to comply with the specifications of the telecommunication network.
As previously mentioned, the power drawn had heretofore been unusable by terminal interface devices, such as modems, since older terminal interface devices required an amount of power for operation beyond what was available. With miniaturization and development of lower power designs, the available power from, for example, the POTS is sufficient to be employed for useful power to electronic components on a network interface device. However, the fluctuation of available line side power is still problematic. The network interface device cannot depend on a variable power source, furthermore, the modem may not introduce noise onto the line side of the communication network which prevents attempts to regulate line side power.
Yet another problem in the realm of data transmission devices is the varying telecommunication interface specifications. The similarity of the network jacks or interface devices connecting the computer to the communication network is the source of considerable confusion. Attempts to connect an analog modem to the phone jack of a digital system result in excessive line current that can fuse the low power circuitry of the modem. To prevent this type of hardware meltdown, some communication programs will display a generic error message, alas the programs do not provide a description of what causes the error. Leaving the user to speculate what the generic error message was indicating. Often the generic error message will only be displayed when the user runs the proprietary communication software to initiate the modem connection. If third party software makes the communication request to use the modem, the error message may not even be displayed to the user. In many cases the damage is done before the user is even aware of the digital line. What is needed is a system that will indicate the presence of excessive line current at the point of connection, so action may be taken before the user""s modem is damaged. Additionally, a device that indicated the presence of excessive line current and automatically protected the interface would be an improvement over the prior art.
As previously indicated, most communication applications direct the digital device to send a message to the user via monitor screen or an audio transducer and then place the modem back on hook to prevent damage to the interface device once excessive line current is detected. As this is a generic error message no true indication is given to the user that an incorrect line is connected. Even once the warning indication is detected, many communication programs will generate a message indicating an error, with no description of what the error provided, thereby leaving the user to speculate on the meaning of the error message. Thus, what is needed is a device that will provide the user with an indication of an incorrect line interface. Specifically, digital lines may damage and even destroy analog modem connections. Such an indicator located on the modem would allow the user to recognize the improper digital connection and avoid destruction of the modem or the attachment circuit.
Thus, what is needed is an apparatus for efficiently utilizing available power in a telecommunication system to more efficiently manage scarce on-board battery power from a portable device such as a portable computer by utilizing available line side power from the telecommunication network during interaction therewith.
What is also needed is an inexpensive system for compatibly interfacing with the high power specifications of legacy telephone networks without reducing the overall reliability of the system, specifically indicating to the user, at the point of interface, if there is excessive line current present in the connection without using battery power for the indicator. This system should economically absorb the requisite power from the legacy telephone equipment as required by the telephone network specification and dynamically adjust the voltage and current drawn from the interface of a terminal as presented over a telephone network.
It is therefore an object of the present invention to provide an efficient power management circuit for incorporation into a terminal or network interface device, (e.g., a modem), that utilizes available line current from a communication network, (e.g., a telephone network), in order to adequately power line status indicators on the network interface device with minimal power impact on the digital device (e.g., a computer and attached computer battery).
It is yet a further object of the present invention to provide a system for efficiently managing the voltage and current specifications imposed on terminal equipment in a telephone network.
It is therefore a further object of the present invention to provide a power circuit for incorporating into a network interface device, such as a modem, that is compatible in various international environments that employ varying communication network specifications including differing line or hold current levels to signal an off-hook condition.
It is yet a further object of the present invention to provide a system for efficiently managing the power-sinking requirement that terminal equipment must present to a telephone network.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims.
To achieve the foregoing objects, and in accordance with the invention as embodied and broadly described herein, a power circuit apparatus for improving upon the architecture and power management of a terminal equipment device, such as a modem, is presented. The power circuit apparatus is deployed in portable environments wherein power management is critical. The power circuit apparatus includes a circuit capable of absorbing or sinking excess power that must be absorbed by the terminal equipment, such as a modem, in order to fall within the compliance specifications propagated by the host telephone network.
As previously mentioned, modem standards require network interface devices to function in compliance with the legacy handset device specifications. This creates the inefficient requirement for the network interface device to sink or dissipate power from the line side power, while using valuable battery power to indicate the line type and off-hook status. By using the hold or line side current from the line or communication network side to power the indicator circuitry, the inefficiencies associated with dual circuitry for power dissipation and line status indicators are minimized.
The circuit of the present invention, in its preferred embodiment, is comprised of an indicator module powered from available line side current derived from the communications network and regulated by the terminal interface device""s hold circuitry. When the hold circuitry either detects a xe2x80x9cringxe2x80x9d signal as dispatched from the communication network or when the digital device signals the network interface device (e.g., modem) to open a channel with the communications network for originating a session, the network interface device goes xe2x80x9coff-hook.xe2x80x9d As recalled from above, the off-hook condition signals to the communication network by drawing or sinking a requisite amount of line current, commonly called hold current or line current, from the communication network.
The voltage across the communication network terminals (e.g., tip and ring in the POTS environment) is used to power a status indicator in the network interface device. Any excess current from the voltage regulator is absorbed by the shunt regulator. Typically, the indicator is a light emitting diode (LED), but auditory and tactile indicators may also be used. Most LEDs will burn out if more than 20 mA are passed through them. As some communication network standards require circuits to sink at least 120 mA of line current the voltage regulator protects indicator circuitry from damage. As previously, mentioned the presence of excessive line current can damage the terminal interface device. Excessive line current may also be an indication that the line is really a digital phone line. Due to the dangers of excessive line side power, the present invention provides an indicator to sense excessive line current and digital lines.
Whenever a low line side current condition occurs the indicator may alter its display, for example the LED will suffer in brightness with reduced line side power. Generally, low line side power is not too great of a problem, since most line current levels are at least 15 mA or greater, however, there are some areas that may drop as low as 10 mA. In this situation a pulse module can store line side power until a periodic burst of power within the indicator operating range can be generated. If the indicator is an LED, the burst will cause the indicator to flash or blink, but the LED""s brightness will not be noticeably reduced. In fact, the pulse itself becomes an indicator of the presence of low line side current.
The present invention also accommodates the multinational nature and use of modem network interface devices by incorporating a programmable xe2x80x9choldxe2x80x9d current sub-circuit that may be programmably altered to conform with varying national standards relating to the requisite hold current that must be drawn from the communication network to signal an off-hook condition.
These and other objects and features of the present invention will be more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth herein.